TR4 like a bolt from the blue

Lightning strikes frequently hit banana plants in North Queensland causing leaf damage that looks similar to TR4 symptoms. Growers are urged to report all suspect plants and not assume electrical storms are the cause of damage. Visiting Montpellier SupAgro University student Kévin de Cozar reports.

After an electrical storm, growers may find individual or groups of banana plants in their paddocks that they suspect have been damaged by lightning strikes.

However, some of the symptoms produced by electrical strikes are very similar to those seen in plants infested with Panama disease Tropical Race 4 (TR4).

This means growers should report to Biosecurity Queensland any plants that appear to have TR4 symptoms, even if they think the damage has been caused by lightning. However, it may be useful for growers to be aware of the type of plant damage caused by lightning and some of the differences to TR4 damage.

Although banana plants are particularly vulnerable to lightning strike, there are very few published accounts or illustrations of the damage caused to bananas.

Steam and shock waves

Lightning strikes happen because banana plants contain a large amount of water which is charged with ions and therefore able to conduct electrical current. Lightning produces high temperature and pressure, resulting in plant damage.

There are two mechanisms for lightning to affect banana plants. The first is when plant fluids convert to steam, burning plant cells and tissues and causing the leaves to wilt and die.

The second mechanism is shock waves caused by high pressure that wreck the internal structure of the plant and can split the trunk. Lightning usually affects a group of plants by heating up the soil water.

Symptoms of lightning include wilting and yellowing of the leaves – something also seen in Panama-affected plants.

However, other symptoms can beobserved that may distinguish lightning-affected plants from Panama infestations. For instance, the symptoms may appear more rapidly and include burnt internal tissues and cooked roots.

The pseudostem of lightning-affected plants lacks the characteristic vascular staining found in Panama-affected plants. Another difference may be that lightning is likely to affect adjacent plants all at the same time, whereas Panama disease may affect plants over a period of time.

Banana growers should be aware of the potential for plants to be damaged by lightning strike. However, in view of the TR4 outbreak identified in North Queensland in March, they should not dismiss instances of plant damage as being due to lightning but report all suspect plants.